PROGRAM SUMMARY The local food environment?or where people obtain their food and beverages?may have dramatic implications for population health and health behavior. Yet, the links between the local food environment and population health are rife with complexity. For instance, evidence supports that the health behavior of food and beverage purchasing can be influenced by environmental features, such as food availability in the store, but also individual features, such as weight status and economic resources. Additionally, what is made available in food stores can be influenced by what customers purchase, manager characteristics, such as their perceptions of customer demand, and beyond store features, such as the availability of food distributors. This broad arrangement of interacting, multi-level, and discipline-crossing factors indicates a complex system with implications for understanding how to intervene to improve population health and behavior. To date, the majority of dietary-related population health and food environment research has had limited consideration for this complexity. Leveraging cutting-edge system science approaches, such as agent-based modeling, has the potential to capture the dynamics among these multi-level factors and generate insights into the most salient mechanisms to target with interventions and policies. Thus, I am seeking this Pathway to Independence Award in order to gain the additional training and mentorship required to establish an independent research program that rigorously investigates these complex, reciprocal, and dynamic drivers in the local food environment for population health. To achieve this goal, a multifaceted training plan will occur during the award's mentored phase to gain additional skills and knowledge in: (1) system science modeling, (2) food environment research, and (3) behavioral economics. The aims of the research during the award's independent phase are to: (Aim 1) describe the factors that influence the relative healthfulness of food and beverages available and purchased, as perceived by different stakeholder groups; (Aim 2) develop, test, and validate systems science agent-based models that capture the multi-level components and dynamic interactions contributing to population patterns of the healthfulness of food and beverages purchased and made available in stores; and (Aim 3) investigate the mechanisms that lead to observable patterns in customer food and beverage purchasing and healthy-to- unhealthy food availability. In addition to collecting foundational qualitative data from stakeholder groups, the proposed research will leverage an existing dataset of longitudinal observational and survey data from the NIH- funded STaple foods ORdinance Evaluation (STORE) Study. Together, the proposed training and research activities will prepare me to successfully compete for subsequent R01 funding that will test interventions and policies recommended to improve the healthfulness of the U.S. food environment and dietary-related population health.